SIMULATION OF INSTABILITY GROWTH-RATES ON THE FRONT AND BACK OF LASERACCELERATED PLANAR TARGETS

The ability of an inertial confinement fusion target to achieve igniti on and burn depends critically upon controlling the,growth of hydrodyn amic perturbations originating on the outer ablator surface and the in ner deuterium-tritium (DT) ice. The MIMOZA-ND code [Sofronov et al., V oprosy Atomnoy Nauki i Tehniki 2, 3 (1990)] was used to model perturba tion growth On both sides of carbon foils irradiated by 0.35 mu m Ligh t at 10(15) W/cm(2). When an initial perturbation was applied to a las er irradiated surface, the computational instability growth rates agre ed well with the existing theoretical estimates. Perturbations applied to the rear side of the target for wavelengths that are large compare d to the thickness (d/Lambda much less than 1) behave similarly to the perturbations at the ablation front. For d/Lambda greater than or equ al to 1, the shorter the wave length is, the faster the decrease of th e growth rate of the amplitudes at the interface (and the mass flows) as compared to the perturbations at the ablation front. This is due to the Richtmyer-Meshkov instability-induced transverse velocity compone nt. The time of Rayleigh-Taylor instability transition to the nonlinea r phase depends on the initial amplitude and is well modeled by an inf initely thin shell approximation. The transverse velocity generated by the Richtmyer-Meshkov instability causes the interaction of Lambda = 10 mu m and Lambda = 2 mu m wavelength modes to differ qualitatively w hen the perturbations are applied to the ablation front or to the rear side of target. (C) 1998 American Institute of Physics.